1. Field of the Invention
The present invention relates to semiconductor wafer polishing and, more particularly, to improved polishing pads to more efficiently polish wafer surfaces and decrease wafer polishing cost.
2. Description of the Related Art
In the semiconductor chip fabrication process, it is well-known that there is a need to polish a semiconductor wafer. This polishing is typically accomplished by a chemical mechanical polishing (CMP) process. Generally, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material grows. Without planarization, fabrication of further metallization layers becomes substantially more difficult due to the higher variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then, metal CMP operations are performed to remove excess metallization.
During CMP, a semiconductor wafer is polished by use of a polishing material, such as a belt or pad, and a solution known as a slurry. The polishing material is typically made from some hydrophilic polymer such as polyurethane. A more detailed discussion regarding polishing pads is stated below. The slurry is generally made up of an aqueous solution with metallic or non-metallic particulates such as, for example, aluminum or silica abrasives that create the added friction needed for the polishing process. In one example of a CMP process, a polishing pad is put in motion (rotated or moved in a conveyer belt fashion) and a slurry solution is applied and spread over the surface of the polishing pad. Once the polishing pad having slurry on it is moving at a desired rate, the wafer is lowered onto the surface of the pad. In this manner, the wafer surface that is desired to be planarized is substantially smoothed, much like sandpaper may be used to sand wood.
Currently available polishing pads, typically polyurethane foam, are limited in effectiveness and consistency because they readily absorb moisture. In use, polishing pads are in continuous contact with aqueous slurries and cleaning solutions. Moisture absorption affects the performance of polishing pads in the following two ways:
1) Softening, swelling, or loss of rigidity through physical and chemical degradation, resulting in reduced planarizing effectiveness and reduced lifetime of the polishing pad,
2) Gradual changes in pad properties and integrity during use, resulting in unsteady and inconsistent performance.
Previous attempts to make polishing pads with reduced moisture absorption or with increased resistance to degradation have been limited because the pads are too hydrophobic, resulting in poor wetting, inefficient slurry distribution, and reduced or varying removal rates.
Broadly speaking, this invention fills these needs by providing a moisture resistant polishing pad with additives to improve wetting of the pad surface for good slurry distribution. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a polishing pad for use in chemical mechanical polishing (CMP) is disclosed. The polishing pad has a pad surface for polishing wafer surfaces. The pad surface is composed of a polymeric matrix material. The polishing pad also contains a polymeric additive which is defined in the polymeric matrix of the pad surface and in cells of the pad surface. The polymeric additive may include one of a polyurethane, a polyamide, a polyester, a polyacrylonitrile, a polyacrylate, a polymethacrylate, a polyvinylchloride, and a polyvinylidene chloride. The polymeric additive is configured to be hydrophilic so that the pad surface is wettable to enable improved slurry distribution over the pad surface.
In another embodiment, a polishing pad for use in chemical mechanical polishing (CMP) is disclosed. The polishing pad has a pad surface for polishing wafer surfaces. The pad surface is composed of a relatively non-polar polymeric matrix material. An additive is defined in the polymeric matrix of the pad surface and in cells of the pad surface where the additive is a surfactant. The additive is hydrophilic so that the pad surface is wettable which enables improved slurry distribution over the pad surface.
In yet another embodiment, a polishing system including a polishing pad for use in chemical mechanical polishing (CMP) is disclosed. The polishing pad has a pad surface for polishing wafer surfaces. The pad surface is composed of a polymeric matrix material which is either a thermoplastic material or a cross-linked material. A relatively polar polymeric additive is defined in the polymeric matrix of the pad surface and in cells of the pad surface. The additive is one of a polyurethane, a polyamide, a polyester, a polyacrylonitrile, a polyacrylate, a polymethacrylate, a polyvinylchloride, and a polyvinylidene chloride. The additive is also hydrophilic so that the pad surface is wettable which enables improved slurry distribution over the pad surface. The polymeric matrix material also absorbs less than 4% moisture by weight. The thermoplastic material used to make the polymeric matrix material is selected from the group consisting of a polytetrafluoroethylene material, a polyethylene material, an acrylonitrile butadiene styrene (ABS) material, a polypropylene material, a fluoronated polymer material, a polyurethane material, a thermoplastic elastomer material, and a polycarbonate material. The cross-linked material used to make the polymeric matrix material is selected from the group consisting of a polyurethane material, a phenolic material, an epoxy material, a natural or synthetic rubber material, and a thermoset material.
In another embodiment, a polishing pad is disclosed. The polishing pad has a pad surface for polishing wafer surfaces where the pad surface is composed of a polymeric matrix material. The polymeric matrix material includes one of a thermoplastic material and a cross-linked material. The polymeric matrix material is defined by cells that extend into the pad while some cells at the pad surface define invaginated features for receiving the slurry. A polymeric additive is defined in the polymeric matrix of the pad surface and in the cells of the pad surface where the polymeric additive includes one of a polyamide and a polyester. The additive is made to be hydrophilic such that the pad surface is wettable to enable improved slurry distribution over the pad surface. The thermoplastic material used to make the polymeric matrix material is selected from the group consisting of a polytetrafluoroethylene material, a polyethylene material, an acrylonitrile butadiene styrene (ABS) material, a polypropylene material, a fluoronated polymer material, a polyurethane material, a thermoplastic elastomer material, and a polycarbonate material. The cross-linked material used to make the polymeric matrix material is selected from the group consisting of a polyurethane material, a phenolic material, an epoxy material, a natural or synthetic rubber material, and a thermoset material.
The advantages of the present invention are numerous. Most notably, by creating a hydrophobic polishing pad which can be wetted, wafer polishing efficiency can be improved and wafer polishing costs may be lowered. The claimed invention reduces the problems of a polishing pad absorbing too much moisture and losing structural integrity. Therefore, the present invention allows more CMP operations to be conducted before the polishing pad must be changed thus increasing CMP processing output and lowering costs of CMP processing by increasing the life of each polishing pad.